1. Field of Invention
The present invention generally relates to a method for treating and decoding data signals in optical storage media, and more particularly, to a method for pre-treating the data signals and decoding the data when they are read out from the disc.
2. Description of Related Art
In order to accommodate the characteristic of the disc, and to increase the reliability of read disc information, the data are treated by an Eight to Fourteen Modulation (EFM) and a Reed-Soloman code modulation process when they are stored in the compact disk (CD), and the sequence for storing the data is amended in an interleaved manner. In order to read the data from the CD disc, at first, the laser beam reflected by the CD is reacted so as to obtain radio frequency data (RF DATA), and to generate a digital data signal DSEFM and a clock signal EFMCLK according to the RF DATA. Then, these two signal data are decoded by using the EFM process, so as to perform the subsequent decoding process for the CD information.
The CD disc stores information in a manner that changes the CD″s current burning status in the CD disc when recording data “1” and not changing the CD″s current burning status in the CD disc when recording data “0”. The so-called EFM process converts 8-bit data into 14-bit data, the data after processed by the EFM process are then stored in the CD disc. The 14-bit data after processed by the EFM process complies with a basic rule, i.e., the duration of the same burning status stored in the CD disc must be greater than or equal to 3 periods of EFMCLK and smaller than or equal to 11 periods of EFMCLK. In other words, the signal waveform of the DSEFM is not changed during 3 periods of the EFMCLK, and the signal waveform of the DSEFM must be changed within a duration less than or equal to 11 periods of the EFMCLK. On the perspective of 14-bit data, the number of data “0” appears in two contiguous data “1” is greater than 2 and less than 10.
The principle of the EFM process mentioned above is also applied in the current generation DVD (Digital Versatile Disc). However, the 8-bit to 14-bit modulation process is changed to an 8-bit to 16-bit modulation process, and the rule is changed to the duration of the same burning status stored in the DVD must be greater than or equal to 3 periods of EFMCLK and smaller than or equal to 11 periods of EFMCLK.
Since the data storage density of the DVD is very high, and the reading speed of the CD driver currently used is getting higher now, plus the CD is characterized that it is easily scratched. Therefore, during the process of reading out data from DVD, it is very possible to generate 16-bit data, which violates the modulation rule mentioned above. If the data are sent to the subsequent demodulation module directly for processing without being processed by using adequate CD information decoding method and apparatus first, the reliability of the data reading deteriorates and the “picky disc” or “disc error reading” problem occurs.